1. Nmap - map your network and ports with the number one port scanning tool. This tool features powerful NSE scripts that can detect vulnerabilities, misconfiguration and security related information around network services.

2. OpenVAS - open source vulnerability scanning suite manages all aspects of a security vulnerability management system from web-based dashboards.

3. OSSEC - host-based intrusion detection system or HIDS is easy to setup and configure. OSSEC has far reaching benefits for both security and operations staff.

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BackTrack is a Linux based security distribution for penetration testing. This cyber security tool is great to tighten your security needs and comprises more than 300 OSS tools categorized into different areas.